Radical prostatectomy (RP) is a commonly used treatment option for localized prostate cancer. Unfortunately, the procedure carries a risk of post-surgical complications including a high risk of erectile dysfunction (ED). According to The Prostate Cancer Outcomes Study, virtually all men experience ED after surgery, including a profound loss of nocturnal erections. The Prostate Cancer Outcomes Study further reveals that 60% of men experienced self-reported ED 18 months after RP, and only 28% of men reported erections firm enough for intercourse at a 5-year follow-up. The main pathophysiological mechanism behind this is damage to the cavernous nerves (CN). Consequently, the mechanisms that facilitate cavernosal oxygenation fail; fibrosis ensues and leads to cavernosal smooth muscle apoptosis. Whereas neuropraxia may be reversible, the penile fibrosis resulting from poor oxygenation permanently damages cavernosal function and produces chronic ED. Accelerated wound healing and nerve growth would preserve penile anatomy and corporal smooth muscle and potentially reduce the time patients experience ED following RP. However, there are at present no clinically approved strategies for this procedure. Several promising studies in animal models have used gene therapy approaches, usually involving overexpression of ?nerve growth factors.? Clinical translation of these gene therapy approaches will be hampered by safety issues over the use of viral vectors or transformed stem cells in a ?benign urological disease? as well as concerns over the ease of application. In addition, there are no orally or topically administered therapeutics that reliably elicit an erection in men with RP-induced ED. Our goal is to develop a novel therapeutic that enhances EF after RP via RNAi-mediated silencing of the microtubule severing enzyme, Fidgetin-like 2 (FL2). Preliminary results in an animal model of RP demonstrate that FL2 can be targeted by nanoparticle-delivered siRNA to dramatically and predictably recover EF. FL2 acts through mechanisms dramatically different from other genes/proteins/factors currently being investigated; the experiments presented in this application represent the first reported success of siRNA in treating ED associated with RP. In addition, our recent preliminary findings indicate that a polyplex-based carrier (?wafer?) of FL2-siRNA is at least as effective as FL2-siRNA-np in restoring EF in an animal RP model. In Specific Aim 1 we will compare a range of concentrations of FL2-siRNA incorporated in a wafer formulation for efficacy in restoring EF following CN injury (transection). Finally, in Specific Aim 2, we will perform toxicity studies to provide evidence of safety for the different siRNA concentrations. Thus, at the end of the project, we will have identified the siRNA-wafer formulation that restores EF and is safe for further IND-enabling studies.